Sound-producing device



y 1930. Q c. R. HANNA 1,768,903

SOUND PRODUCING DEVICE Filed March 25, 1927 45 Fz'yZ.

WITNESSES: INVENTOR A! 76 W Clinton 1?. Hanna UNITED .STATES PATENT"OFFICE- cnm'ron n. mmu, or swrssvnn, rmmsnvam, assienoia. 'rownsrmenousn mare a uanurac'rumne couramr, a conroaarron or rnmzsnvmmsouim-rnonucme DEVICE My invention relates to sound-producing devicesand more particularl to devices of the type known as loud spe rs.

One object of my invention is to provide an electro'dynamically operatedsound-producing device in which} the sound-output pressure is at alltimes proportional to the [energizing current, for large values ofcurrent.

Another object of my invention is to so design a loud speaker that thediaphragm thereof shall produce uniform air velocity in the throat ofthe horn over a wide range of sound frequencies, provided the effectivecurrent in the. actuating means therefor remains constant.

Another object of my invention isto pro- ,vide an electro-dynamicsound-producing device articularly adaptable for use with a I),hornaving an ex onential curvature.

A still further 0 ject of my invention is to provide an improvedmagnetic circuit for a sound-producing device of the type described.

In a copending application filed by Joseph Slepian and Clinton R, Hanna,Serial No. 690,405, on February 4, 1924, and assigned to theWestinghouse Electric and Manufacturing Company which has matured intoPatent No. 1,623,561, there is disclosed an exponently curved hornparticularly adaptable for use in connection with loud-speakers such asare employed in radio reception and in public-address systems. In theHanna and Slepian application, it is pointed out that, by utilizing ahorn of the shape disclosed, it i is possible to maintain a constantratio between the sound pressure radiated from the horn and the averageair velocity at the throat of horn, over a wide range of frequencies.

By the present invention, which isf'in the nature of an improvement overthe invention disclosed in my former application, I have provided adiaphragm-actuating mechanism that is peculiarly adaptable for usein'con nection with an exponentially curved horn. By pro rly proortioning the relative mass and sti ness of t e various component artsof my actuating mechanism, I have pro uced a device that gives a uniformair v ocity, in

objects and advantages t ereof, will best be understood by reference tothe following de- 1 scription taken in connection with the ac-,companying drawings, in which Figure 1 is a side elevational view,partly in section, of a preferred embodiment of my invention,

Fig. 2 is an end elevational view,

Fig. 3 is a top plan view of a preferred type of diaphra ,and

Fig. 4 is a sectional view of the diaphra taken alon a linecorresponding to the ine IV-IV 0 Fig. 3. y

Referring specifically to Figs. 1 and 2 the magnetic portion of mimproved loud speaker preferably comprises a central pole piece 1, abridging member 2 and two L- shaped magnets 3 and 4. 'ihe bridgingmember 2, which is made of a magnetic material having a highpermeability, is provided with a centra openin into which projects areduced, cylindrica portion of the central pole piece 1. The ole iece J.is maintained in position centra ly of the opening in order to define anair-gap, the holding means therefor comprising a non-magnetic collar 5frictionally mounted thereon and fastened to the under side of thebridging member 2 by a 'lurality of screws 6.

The L- aped permanent magnets 3 and 4 which, together with the centralpole piece 1, are preferably made of cobalt-steel, are so arranged thatthe ends of the longer portions 7 and 8 thereof abut the under side ofthe bridging member 2, while the ends of the shorterv portions 11 and 12are held in firm contact with the lower portion of the central polepiece. The L-shaped magnets are clamped firmly against the central polepiece 1, and against shoulders 13 and 14 provided 100 on thebridging'member, by means of a plurality of U-shaped members 15 and 16,tension being exerted thereon through a plurality of tie-rods 17 and 18.

A guard element 21, provided with upturned edges 22 and 23, and withspring portions 24 and 25, is mounted on the lower end of the centralpole piece 1 by means of a screw 26 and serves to prevent movement ofthe lower ends of the L-shaped ma ets with respect to the saidpole-piece. e spring portions 24 and 25 of the guard element exert anupward pressure on the L-shaped magnets, thus tendin to maintain the uper ends thereof in rm contact with the ridging member 2.

A mounting element 27 of non-magnetic material such as brass or thelike, and which may or may not be circular in shape, is mounted on thebridging member 2, and is held firmly in position by a plurality ofscrews 28. The mounting element is provided with a centrally locatedcircular opening 31, slightly larger in diameter than a diaphragm 32which is suspended therein from a flexible annulus 33 that, in turn, istightly clamped between a shoulder 34 surrounding the opening 31 and anon-magnetic horn-supporting element 35. A plurality of screws 36maintain the horn-supportin element 35 in position on the mounting eement 27, and provide the necessary pressure to hold the annulus 33tightl clamped.

The under sur ace of the horn-supportin element 35 is provided with aplurality o conical protuberances 37 and 38 which cooperate withdepressions in the diaphragm 32 to define an air chamber 41, thedimensions of which are very accurately pre-determined.

A coil supporting form 42, on which is wound a coil 43 adapted to carrycurrents representing the sounds to be reproduced, is suspended from theunder surface of the diaphragm by a plurality of arms 44. These arms,which will later be referred to collec tively as the spider, have adefinite amount of stifi'ness, the value of which is definitelypredetermined, and which is hereinafter designated as S In the drawing,the circular air-gap between the central pole piece 1 and the bridgingmember 2 is greatly exaggerated, in order that the coil supporting form42 and the winding 43 may be more clearly visible. In an actualembodiment of my invention this air gap is about 1.5 millimeters wide.

The horn-supporting element 35 is provided with a central opening 45having a surrounding raised portion or collar. Interiorly of the openingis a circular shoulder 46 on which is supported the throat 47 of anexponential horn, a plurality of set screws 48 passing through thecollar andcontacting a ferrule 51 carried by the horn, serving to holdthe same in fixed position relative to the opening.

A dome-like guard element 52, rovided with perforations, also rests uponthe shoulder 46, and is held in position by the lower end of the horn.This element prevents foreign objects from being so inserted into thehorn as to cause injury to the diaphragm.

The manner in which the leads are brought out from the coil forms nopart of the present invention. In the drawing, Fig. 1, leads 53 and 54are shown as passing down through openings 55 and 56 drilled in thebridging member. This arrangement, however, is merely illustrative, itbeing perfectly feasible to pass the leads up and over the bridgingmember 2, bringing them out through the space between the sides thereofand the lower e ge of the central opening 31 in the mounting member 27.

he spaces between the sides of the bridging member 2 and the lower edgesof the central openin in the mounting member 27 also have the a ditionalfunction of preventing the building up of any back-pressure on thediaphragm when it is in motion. This is an important feature, inasmuchas it is desirable that the diaphragm shall be impeded as little as1ppssible, on the side opposite the horn.

ferring to Figs. 3 an 4, the diaphragm 32 is preferably made of anextremely light material, such as aluminum, and is extremely thin inorder that it may have a very low mass. The necessary internal stiffnessis secured by embossing the diaphragm with a plurality of cone-shapedepressions 57, which mutually intersect on hyperbolic lines.

By embossing the diaphragm with a plurality of conical depressions, allof which have curved surfaces, all tendency for the diaphragm to vibratenodally is obviated. True piston, or plunger action can, therefore, beobtained by applying the driving force to the apices of certain of thecones, with the assurance that the diaphragm will neither buckle norvibrate in 'any manner except as a whole.

The mounting annulus 33, preferably of high-grade rubber, or thelike,'is firmly affixed to the periphery of the diagram by a suitablecement.

The coil mounting form 42 is preferably made of aluminum, of a thicknessof not more than .003 of an inch, andmay be provided with a slot 58 toprevent the circulation of eddy currents under potentials inducedtherein when the form is moving in the air gap.

The spider arms 44 may be made integral with the form 42, and they maybe provided with terminating portions 61 adapted to be inserted throughsmall openings in the diaphragm 32 and riveted or soldered in place.

Oxidized or enameled aluminum wire has been found to be the bestmaterial 'for the coil 43, the wire being cemented to the form bycellulose nitrate, or other material.

cal filter, adapted to effectively pass a definite band of soundfrequencies. The rate of flare of the horn, and the area of the mouthopening thereof determine ,the lower cut-off frequency, while the u percut-off frequency is largely determined by the characteristics of themechanical vibratory system.

By properly choosing the various propor tions of the mechanicalvibrating system, the upper cut-off frequency may be made as high asdesired.

The following relations, if adhered to, will give rise to a system whichproduces a constant air velocity in the throat of the horn over a widerange of frequencies:

1. The mass M of the coil 43 and form 42 in grams should together beequal to the mass M of the diaphragm, for the greatest efficiency.

2. The acoustic damping, or mechanical resistance, R, of the horn uponthe diaphragm, must equal,

d a M where f equals the upper cut-off frequency. 3. The stiffness, S ofthe spider, and S of the air chamber, should equal dynes r7 M and Z'IrfM Sec respectively. 7

The term stiffness, as applied to the airchamber, refers to the reactionforce on the diaphragm, per unit deflection thereof, when the opening tothe horn is closed, and is preferably expressed in dynes per centimeterof deflection.

Considering the diaphragm to act as a piston, the acoustic damping, R,is 41.2 f in of well-known physical and mechanical theories andformulae. The stiffness, S of the air chamber, is the totalreactionforce on the diaphragm per unit deflection of the diaphragm whenthe orifice of the horn is closed. The valued the stiffness S may becalculated by the employment of ordinary and well-known laws relating tothe pressure and volume of gases.

The overall efliciency of a number of loud speakers constructedaccording to my invention has been calculated, and verifiedexperimentally. careful designs it has been found that, 1n the range offrequencies where the response is uniform, the motion of the w diaphragmis so large as to generate a backvoltage substantially one half as greatas the voltage required to overcome the clamped impedance of the coil,i. e., the impedance of the coil when motion is not permitted. Undersuch conditions, the efficiency of the device is approximately 33 A, percent, considerably greater than the efliciency of an other high-qualityloud speaker with whic I am familiar.

. Although I have illustrated and described a specific embodiment of myinvention, many modifications thereof are possible. M invention,therefore, is not to be limite in so far as is necessitated by the priorart, and by the spirit of the appended claims.

I claim as my invention:

1. In combination, a diaphra anactuating coil carried by a form, an aplurality of resilient arms integral with said form for attaching it tosaid diaphragm.

2. In combination, a diaph m, an actuating coil carried by a form, an aplurality of resilient means integral with said form for connecting saidform and said diaphragm, the mass of said coil and form being equal tothe mass of said diaphragm.

' 3. In combination, a diaphragm, an actuating coil therefor carried bya non-magnetic form, and a plurality of resilient arms integral withsaid form for attaching it to said diaphragm.

4. In combination, a diaphragm, an actuating coil therefor carried by anon-magnetic except form, and a plurality of resilient arms inte saiddiaphragm.

6. In a sound-reproducing device, a diaphragm having a plurality ofconical depressions therein, and an air. chamber havlng a wall providedwith conical raised portions adapted to 00-0 erate with saiddepressions.

7. In a soun -reproducing device, a diaphragm having a plurality ofconical depressions eccentric with respect to one another, and an aircham er having a wall provided with conical raised portions adapted toco-operate with said depressions.

8. In a sound-reproducing device, a diaphragm having aplurality ofconical depressions therein, the bases of said depres-,

sions intersectin along hyperbolae.

9. In a soun -reproducmg device, a diaphragm having a plurality ofconical, mu-

tually intersecting depressions therein, and an air chamber having awall provided with conical protuberances adapted to co-operate with saiddepressions.

10. In a sound-re reducing device, a magnetic circuit comprising acentral pole piece having a reduced end portion, a plurality of L-shapedpermanent magnets, a bridging member provided with an opening toaccommodate said reduced portion and means for maintaining said polepiece in fixed relation to said bri ging member. 7

11. In a sound-reproducing device, a magnetic circuit comprising acentral pole piece having a reduced end portion, a plurality of L-shapedpermanent magnets, a bridging member provided with an opening, means formaintaining said reduced end portion substantially concentric with saidopeningv and means for maintainin said L-shaped magnets in contactvvithsaid pole pieceand said bridging member.

12. In a sound-reproducing device, a pole piece, a magnetic circuitcomprising a bridging member of magnetizable material provided with anopening in which is positioned a reduced end portion of said pole piece,a plurality of L-shaped permanent magnets, means including a pluralityof collar-members and a plurality of tie-rods for so removablypositioning said permanent ma ets in contact with said pole piece andsai brid ing member that the reduced end of said po 6 piece and bridgingmember assume opposite 5 polarities.

13. In a sound-reproducing device, a diaphragm having a plurality ofconical depressions therein, a coil supporting form, and resilient meansconnected between said form and the apices of certain of said conicaldepressions.

14. In a sound-reproducing device, a diaphragm having a plurality ofconical depressions therein, a coil-supporting form,

and resilient means connected between said form and the apices ofcertain of said conical depressions, said resilient means being integralwith said coil-supporting form.

15. In an acoustic device, a diaphragm actuating means thereforconnected thereto through resilient means, an air chamber, the stiifnessof said resilient means being substantially one half that of said airchamber.

In testimony whereof, I have hereunto subscribed my name this 21st da ofMarch, 1927.

CLINTON R. HANNA.

